OBJECTIVE: To identify demographic, biological and dietary factors associated with endometriosis in a group of Sri Lankan women. METHODS: A case-control study was conducted at two tertiary care hospitals. Women with endometriosis (n=150) were compared with age-matched controls (n=150) with no evidence of endometriosis, both confirmed by laparoscopy or laparotomy. Data were collected using an interviewer-administered questionnaire and a food frequency questionnaire. Means were compared using paired t-tests and chi square tests and odds ratios (OR) were used to determine associations between dichotomous variables. Conditional logistic regression analysis was done to adjust for potential confounding variables. RESULTS: The ethnic distribution, age at menarche, average length of the menstrual cycle and body mass index were similar in the two groups. The mean (+SD) duration of menstruation in the cases (4.11±0.11 days) was significantly higher than in the controls (3.47±0.16 days, p=0.01). Endometriosis was commoner among those with regular menstrual cycles (OR=3.108; 95% CI=1.473-9.627) and those having an education above Advanced Level (OR=1.729; 95% CI=1.041- 2.87). None of the food items was significantly associated with endometriosis. The risk of endometriosis was 2.084 times greater among those with an education above Advanced Level as compared to those having an education below Advanced Level (p=0.021) after adjusting for confounding factors. CONCLUSION: Among Sri Lankan women, endometriosis is commoner among those who are more educated.